The management of river vegetation with particular reference to shading effects of marginal vegetation

Abstract

The causes and effects of historical and recent events in river management are outlined, particularly for the U.K., and put in perspective in relation to the general and ecological needs of the riverine environment rather than single specific requirements. The necessity for, and types of, aquatic plant management in rivers are discussed, and a new technique of aquatic plant control by shade from the vegetation on or near the banks is discussed. The importance of the optimal half-shade condition, allowing some aquatic plant growth rather than the excess growth found in open streams or the barren situation of forest streams, is emphasised. General examples of shading are given mainly for lowland nutrientrich streams and rivers, in which plant control is generally considered to be a necessity. The role and importance of larger vegetation is considered in the lowland and upland landscape, in the riverscape, and in smaller, intensively managed situations. It is pointed out that many of the isolated trees by rivers are only of visual interest and barely help in aquatic plant control. Specific examples of the degree of shade found across different sizes of lowland river are given, together with examples of the visual effects of the types of vegetation which should be allowed to remain, or even be encouraged to grow, by streams and rivers. Preliminary guidelines for the control of aquatic plants by the creation of half-shade conditions are given on the basis of data discussed in the paper.